Integrated circuit device with source/drain barrier

ABSTRACT

Various examples of an integrated circuit device and a method for forming the device are disclosed herein. In an example, a method includes receiving a workpiece that includes a substrate, and a device fin extending above the substrate. The device fin includes a channel region. A portion of the device fin adjacent the channel region is etched, and the etching creates a source/drain recess and forms a dielectric barrier within the source/drain recess. The workpiece is cleaned such that a bottommost portion of the dielectric barrier remains within a bottommost portion of the source/drain recess. A source/drain feature is formed within the source/drain recess such that the bottommost portion of the dielectric barrier is disposed between the source/drain feature and a remainder of the device fin.

The present application is a continuation application of U.S. patentapplication Ser. No. 15/796,968, filed Oct. 30, 2017, which isincorporated herein by reference in its entirety.

BACKGROUND

The semiconductor industry has progressed into nanometer technologyprocess nodes in pursuit of higher device density, higher performance,and lower cost. Beyond merely shrinking devices, circuit designers arelooking to novel structures to deliver even greater performance. Oneavenue of inquiry is the development of three-dimensional designs, suchas a Fin-like Field Effect Transistor (FinFET). A FinFET may beenvisioned as a typical planar device extruded out of a substrate andinto the gate. An exemplary FinFET is fabricated with a thin “fin” (orfin structure) extending up from a substrate. The channel region of theFET is formed in this vertical fin, and a gate is provided over (e.g.,wrapping around) the channel region of the fin. Wrapping the gate aroundthe fin increases the contact area between the channel region and thegate and allows the gate to control the channel from multiple sides.This can be leveraged in a number of way, and in some applications,FinFETs provide reduced short channel effects, reduced leakage, andhigher current flow. In other words, they may be faster, smaller, andmore efficient than planar devices.

Because of the complexity inherent in FinFETs and other nonplanardevices, fabrication techniques are still being developed to reducesize, improve efficiency, and increase speed.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 is a perspective view of a portion of a workpiece according tovarious aspects of the present disclosure.

FIG. 2 is a flow diagram of a method for fabricating a FinFET device ona workpiece according to various aspects of the present disclosure.

FIG. 3 is a perspective view of a portion of a workpiece according tovarious aspects of the present disclosure.

FIGS. 4-9 are cross-sectional views of a portion of a workpiece takenalong a device fin according to various aspects of the presentdisclosure.

FIG. 10 is a cross-sectional view of the portion of the workpiece takenalong a source/drain region according to various aspects of the presentdisclosure.

FIG. 11 is a cross-sectional view of a portion of a workpiece takenalong a device fin according to various aspects of the presentdisclosure.

FIG. 12 is a cross-sectional view of a portion of a workpiece takenalong a device fin according to various aspects of the presentdisclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the disclosure.Specific examples of components and arrangements are described below tosimplify the present disclosure. These are, of course, merely examplesand are not intended to be limiting. For example, the formation of afirst feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations beyond the extentnoted.

Moreover, the formation of a feature on, connected to, and/or coupled toanother feature in the present disclosure that follows may includeembodiments in which the features are formed in direct contact, and mayalso include embodiments in which additional features may be formedinterposing the features, such that the features may not be in directcontact. In addition, spatially relative terms, for example, “lower,”“upper,” “horizontal,” “vertical,” “above,” “over,” “below,” “beneath,”“up,” “down,” “top,” “bottom,” etc. as well as derivatives thereof(e.g., “horizontally,” “downwardly,” “upwardly,” etc.) are used for easeof the present disclosure of one features relationship to anotherfeature. The spatially relative terms are intended to cover differentorientations of the device including the features.

Advances in integrated circuit design and fabrication have deliveredimprovements in circuit speed and efficiency. However, despite newstructures and new fabrication techniques, transistors and other circuitelements still experience losses and inefficiencies. In many cases,parasitic effects, such as leakage, hot carrier injection, tunneling,drain-induced barrier lowering, and others, have a greater impact witheach generation of improvements because the new techniques form smallerdevices that operate at lower voltages. These parasitic effects maywaste energy, produce excess heat, reduce maximum operating frequency,and/or increase minimum operating voltage. In extreme cases, they maylead to premature device failure.

One example is leakage current, the unintentional flow of carriers (suchas when the device is in the off-state) that includes source-to-drainleakage, pn junction leakage, source (or drain)-to-bulk punch through.Because some types of leakage increase as channel length decreases, theleakage current may limit attempts to shrink the size of the device.

To address leakage and other parasitic effects, some examples of thepresent disclosure provide a transistor, such as a Fin-like Field EffectTransistor (FinFET), with dielectric barriers at the base of thetransistor's source/drain features. The dielectric barriers electricallyinsulate the bottommost portions of the source/drain features to inhibitleakage current from flowing around the channel region or from flowinginto the bulk of the substrate. The sides of the source/drain featuresmay be free of the dielectric barrier to permit the flow of carriersthrough the channel region. In contrast to a buried dielectric layer,the dielectric barriers may be physically separate from each other andmay be formed in the source/drain regions exclusively.

The dielectric barriers may reduce multiple types of leakage current,and many examples provide improved efficiency, reduced heat, and/orincreased switching frequency. In some examples, the dielectric barrierspermit forming transistors with smaller channel lengths and therebyimprove device density. However, unless otherwise noted, no embodimentis required to provide any particular advantage.

FIG. 1 is a perspective view of a portion of a workpiece 100 accordingto various aspects of the present disclosure. The perspective view ofFIG. 1 has been sectioned along the longitudinal length of a fin. FIG. 1has been simplified for the sake of clarity and to better illustrate theconcepts of the present disclosure. Additional features may beincorporated into the workpiece 100, and some of the features describedbelow may be replaced or eliminated for other embodiments of theworkpiece 100.

The workpiece 100 includes a substrate 102 with one or more device fins104 formed upon it and separated by isolation features 106. The devicefins 104 are representative of any raised feature, and while theillustrated embodiments include FinFET device fins 104, furtherembodiments include other raised active and passive devices formed uponthe substrate 102. Each FinFET device fin 104 may include any number ofFinFETs that, in turn, each include a pair of opposing source/drainfeatures 108 separated by a channel region 110. As seen in FIG. 1, thesource/drain features 108 and channel region 110 rise above the plane ofthe substrate 102 upon which they are formed and above the isolationfeatures 106. Accordingly, the circuit devices formed on the device fins104 may be referred to as “nonplanar” devices.

The flow of carriers (electrons for an n-channel FinFET and holes for ap-channel FinFET) through the channel region 110 of a FinFET iscontrolled by a voltage applied to a gate stack 112 adjacent to andoverwrapping the channel region 110. The gate stack 112 is shown astranslucent to better illustrate the underlying channel region 110. Theraised channel region 110 provides a larger surface area proximate tothe gate stack 112 than comparable planar devices. This strengthens theelectromagnetic field interactions between the gate stack 112 and thechannel region 110, which may reduce leakage and short channel effectsassociated with smaller devices. Thus in many embodiments, FinFETs andother nonplanar devices deliver better performance in a smallerfootprint than their planar counterparts do.

Despite a FinFET's enhanced control over the channel, it has beendetermined that leakage current may still flow from the source/drainfeatures 108. One avenue for the flow of carriers is out through thebase of a first source/drain feature 108, through the substrate 102underneath the channel region, and in through the base of a secondsource/drain feature 108. This potential leakage path is indicated byarrow 114 in FIG. 1. Because the gate stack 112 does not extend to downto the leakage path, the gate stack 112 may not be able to prevent thisunintended flow of carriers even when the device is in an off-state.Another avenue for the flow of carriers is out from the base of asource/drain feature 108 and through the bulk of the substrate 102 asindicated by arrow 116.

To reduce potential leakage current through base of the source/drainfeatures 108, in some examples, the workpiece 100 includes a dielectricbarrier 118 disposed between the base of each source/drain feature 108and the remainder of the fin 104 that inhibits the flow of carriers. Toallow the normal function of the transistor, the vertical surfaces ofthe source/drain features 108 (such as surface 120) adjacent the channelregion 110 are free of the dielectric barrier 118 so that the verticalsurfaces of the source/drain features 108 physically contact the channelregion 110. This allows carriers to flow through the portions of thechannel region 110 under control of the gate stack 112 while inhibitingthe flow of carriers through the substrate 102, the device fin 104,and/or the portions of the channel region 110 that are not sufficientlyunder control of the gate stack 112.

It is noted that the dielectric barriers 118 may be physically separatefrom each other. In some examples described below, this is because thedielectric barriers 118 are created during the formation of thesource/drain features 108. The process forms each dielectric barrier 118in the region between the respective source/drain feature 108 and theportion of the fin 104 or substrate 102 directly underneath thesource/drain feature 108. In other words, in some examples, thedielectric barriers 118 do not extend underneath the channel region 110.

Exemplary methods of forming FinFETs with a dielectric barrier 118 willnow be described with reference to FIGS. 2-10. In particular, FIG. 2 isa flow diagram of a method 200 for fabricating a FinFET device on aworkpiece according to various aspects of the present disclosure. It isunderstood that additional steps can be provided before, during, andafter the method 200 and that some of the steps described can bereplaced or eliminated for other embodiments of the method. FIG. 3 is aperspective view of a portion of the workpiece 300 according to variousaspects of the present disclosure. FIG. 3 is sectioned along thelongitudinal length of a fin 104. FIGS. 4-9 are cross-sectional views ofa portion of the workpiece 300 taken along a device fin (along plane 302of FIG. 3) according to various aspects of the present disclosure. FIG.10 is a cross-sectional view of the portion of the workpiece taken alonga source/drain region (along plane 304 of FIG. 3) according to variousaspects of the present disclosure. FIGS. 3-10 have been simplified forthe sake of clarity and to better illustrate the concepts of the presentdisclosure. Except where noted, the elements of FIGS. 3-10 may besubstantially similar to those of FIG. 1.

Referring first to block 202 of FIG. 2 and to FIG. 3, a workpiece 300 isreceived that includes a substrate 102 upon which fins 104 are disposed.In various examples, the substrate 102 includes an elementary (singleelement) semiconductor, such as silicon or germanium in a crystallinestructure; a compound semiconductor, such as silicon germanium, siliconcarbide, gallium arsenic, gallium phosphide, indium phosphide, indiumarsenide, and/or indium antimonide; a non-semiconductor material, suchas soda-lime glass, fused silica, fused quartz, and/or calcium fluoride(CaF₂); and/or combinations thereof.

The substrate 102 may be uniform in composition or may include variouslayers. The layers may have similar or different compositions. Forexample, a silicon-on-insulator (SOI) substrate 102 includes aninsulator layer, such as a semiconductor oxide, a semiconductor nitride,a semiconductor oxynitride, a semiconductor carbide, and/or othersuitable insulator materials for electrical isolation. In furtherexamples, the substrate 102 includes layers with different semiconductorlattice arrangements to induce device strain and thereby tune deviceperformance.

The fins 104 are disposed on the substrate 102 and may be formed byetching portions of the substrate 102, by depositing various layers onthe substrate 102 and etching the layers, and/or by other suitabletechniques. The fins 104 may be similar in composition to the substrate102 or may be different therefrom. For example, in some embodiments, thesubstrate 102 may include primarily silicon, while the fins 104 includeone or more layers that are primarily germanium or a SiGe compoundsemiconductor. In some embodiments, the substrate 102 includes a SiGecompound semiconductor, and the fins 104 include one or more layers thatinclude a SiGe compound semiconductor with a different ratio of siliconto germanium.

The workpiece 300 may include gate stacks 112 disposed over channelregions 110 of the fins 104. The gate stacks 112 are disposed on the topsurface of the fins 104 and may also extend along the side surfaces ofthe fins 104. Because the gate stacks 112 surround the fins 104, more ofthe channel region 110 is proximate to the gate stack 112 than in aconventional planar device.

The gate stacks 112 are shown in more detail in FIG. 4. The gate stacks112 are disposed on top of the channel regions 110 of the fins 104 andextend along the vertical sidewalls of the channel regions 110 of thefins 104. In the context of FIG. 4, outline 402 represents the relativeposition of the portion of a gate stack 112 that extends along a sidesurface of the fin 104 out of the cross-sectional plane.

A finished gate stack 112 may include an interfacial layer disposed onthe channel region 110, a gate dielectric disposed on the interfaciallayer, a gate electrode disposed on the gate dielectric, and/or othersuitable elements. However, at this point in the method 200, the gatestack 112 may include placeholder elements. For example, in a gate-lastprocess, the gate stack 112 includes a temporary gate electrode 404 usedas a placeholder during some of the fabrication processes. Thetemporary/placeholder gate electrode 404 is subsequently removed andreplaced with an interfacial layer, a gate dielectric, a functional gateelectrode, and/or other gate elements. A gate-last process may be usedwhen the functional gate materials are sensitive to some fabricationprocesses, such as annealing. Accordingly in some examples, when theworkpiece 300 is received, the gate stacks 112 include placeholder gateelectrodes 404. A placeholder gate electrode 404 may includepolysilicon, dielectric material, and/or other suitable materials. Incontrast, a functional gate electrode that will replace the placeholdergate electrode 404 may include tungsten, aluminum, copper, titanium,tantalum, molybdenum, ruthenium, tantalum nitride, nickel silicide,cobalt silicide, TiN, WN, TiAl, TiAlN, TaCN, TaC, TaSiN, metal alloy,other suitable materials, and/or combinations thereof.

Each gate stack 112 may include a capping layer 406 disposed on a topsurface of the gate electrode 404. The capping layer 406 protects thegate electrode 404 during fabrication processes such as etching. Invarious examples, the capping layer 406 includes a dielectric material(e.g., semiconductor oxides, semiconductor nitrides, semiconductoroxynitrides, semiconductor carbides, semiconductor oxycarbonitrides,etc.), and/or other suitable materials. In one embodiment, the cappinglayer 406 includes silicon carbide.

The gate stacks 112 may also include gate spacers 408 or sidewallspacers disposed on the side surfaces of the gate electrode 404. Similarto the capping layer 406, the gate spacers 408 may protect the gateelectrode 404 and may be used to offset subsequently formed source/drainfeatures and to control the source/drain structure (junction) profile.In various examples, the gate spacers 408 include dielectric materials(e.g., semiconductor oxides, semiconductor nitrides, semiconductoroxynitrides, semiconductor carbides, semiconductor oxycarbonitrides,etc.), and/or other suitable materials, and are different in compositionand etchant sensitivity from the capping layers 406. In one embodiment,the gate spacers 408 each include one or more layers of silicon nitrideand/or silicon oxide.

To form the source/drain features 108 on opposing sides of the channelregion 110, portions of the fins 104 may be etched and the source/drainfeatures 108 may be epitaxially grown in the resulting recesses.Referring to block 204 of FIG. 2 and to FIG. 5, a photoresist layer 502is deposited on the workpiece 300. An exemplary photoresist layer 502includes a photosensitive material that causes the layer to undergo aproperty change when exposed to light. This property change can be usedto selectively remove exposed or unexposed portions of the photoresistlayer in a process referred to as lithographic patterning.

Referring to block 206 of FIG. 2 and to FIG. 6, the photoresist layer ispatterned to expose source/drain portions of the fins 104. In one suchembodiment, a photolithographic system exposes the photoresist layer 502to radiation in a particular pattern determined by a mask. Light passingthrough or reflecting off the mask strikes the photoresist layer 502thereby transferring a pattern formed on the mask to the photoresist502. In other such embodiments, the photoresist layer 502 is exposedusing a direct write or maskless lithographic technique, such as laserpatterning, e-beam patterning, and/or ion-beam patterning. Once exposed,the photoresist layer 502 is developed leaving the exposed portions ofthe resist, or in alternative examples, leaving the unexposed portionsof the resist. An exemplary patterning process includes soft baking ofthe photoresist layer 502, mask aligning, exposure, post-exposurebaking, developing the photoresist layer 502, rinsing, and drying (e.g.,hard baking). The patterned photoresist layer 502 exposes portions ofthe fins 104 to be etched.

Referring to block 208 of FIG. 2 and to FIG. 7, an etching process isperformed on the workpiece 300 to create source/drain recesses 702. Theetching processes may include any suitable etching technique such as wetetching, dry etching, Reactive Ion Etching (RIE), ashing, and/or otheretching methods. In some embodiments, the etching process includes dryetching using an oxygen-based etchant, a fluorine-based etchant (e.g.,CF₄, SF₆, CH₂F₂, CHF₃, and/or C₂F₆), a chlorine-based etchant (e.g.,C₁₂, CHC₁₃, CCl₄, and/or BCl₃), a bromine-based etchant (e.g., HBrand/or CHBR₃), an iodine-based etchant, other suitable etchant gases orplasmas, and/or combinations thereof. In some embodiments, the etchingprocess includes wet etching using diluted hydrofluoric acid (DHF),potassium hydroxide (KOH) solution, ammonia, hydrofluoric acid (HF),nitric acid (HNO₃), acetic acid (CH₃COOH), and/or other suitable wetetchant(s). In some examples, the etchant is selected to etch the fins104 without significantly etching surrounding structures such as theouter materials of the gate stack 112 (e.g., the capping layer 406 orthe gate spacers 408) or the isolation features 106. This may allow theetching to be performed even if the patterned photoresist layer 502 isnot perfectly aligned.

The etching process may recess the fins 104 to any suitable depth asmeasured from the top surface of the channel region 110 of the fin 104to the bottommost point on the surface of the fin 104 withinsource/drain recesses 702 (as indicated by marker 704). In someexamples, the etching process is controlled to stop etching when thesource/drain recesses 702 (excluding the dielectric barriers 118discussed in more detail below) are below the topmost surface of theisolation features 106 (indicated by dashed line 706 because theisolation features 106 may be out of the cross-sectional plane) andaccordingly, the bottommost surface of the gate stack 112 (alsoindicated by dashed line 706). In some examples, the etching process iscontrolled to stop etching when the source/drain recesses 702 (excludingthe dielectric barriers 118) are substantially coplanar with the topsurface of the isolation features 106. In yet further examples, theetching process is controlled to stop etching when the source/drainrecesses 702 (excluding the dielectric barriers 118) are above the topsurface of the isolation features 106.

In some such examples, where a fin 104 extends between about 45 nm andabout 60 nm above the isolation features 106, the etching process may becontrolled to etch to a depth (indicated by marker 704) between about 50nm and about 65 nm from the top of the fin 104. Accordingly in variousexamples, the lowest point on the surface of the fin 104 within thesource/drain recesses 702 is between about 5 nm and about 10 nm belowthe top surface of the isolation features 106 and accordingly, thebottom surface of the gate stack 112. In further examples, the lowestpoint on the surface of the fin 104 within the source/drain recesses 702substantially coplanar with the top surface of the isolation features106. In yet further examples, the lowest point on the surface of the fin104 within the source/drain recesses 702 is between about 5 nm and about10 nm above the top surface of the isolation features 106.

As can be seen in FIG. 7, the etching process may form dielectricbarriers 118 within the source/drain recesses 702. The dielectricbarriers 118 may include a native oxide and/or other dielectric material(e.g., semiconductor oxides, semiconductor, hydroxides, semiconductornitrides, semiconductor oxynitrides, semiconductor carbides,semiconductor oxycarbonitrides, etc.) produced when the etchant andambient chemicals react with the semiconductor of the fin 104. Forexample, the dielectric barrier 118 may include carbon, hydrogen, oroxygen from an etchant; nitrogen from an ambient gas; and/or carbon,hydrogen, oxygen, or nitrogen from remnants of a photoresist. In someexamples, the dielectric barriers 118 include primarily a semiconductoroxide such as silicon oxide, silicon carbon oxide, germanium oxide,germanium carbon oxide, SiGe oxide, SiGe carbon oxide, and/orcombinations thereof. In various examples, the dielectric barrier 118 isa material with between about 0 and about 1 atomic percent of one ormore semiconductors (e.g., Si and/or Ge), between about 30 and about 40atomic percent carbon, between about 10 and about 20 atomic percentoxygen, and between about 20 and about 30 atomic percent hydrogen.Accordingly, in some such examples, the material of the dielectricbarrier 118 is free of any semiconductor.

By using the material formed by etching the fin 104 as a dielectricbarrier 118, some examples save a step of depositing a barrier in asubsequent process. Each fabrication process, (e.g., deposition,annealing, etc.) may contribute to the thermal budget, a limit on howmuch the workpiece can be heated without damage, and eliminating adeposition step may leave more room in the budget for other processes.Furthermore, by forming the dielectric barrier 118 by etching the fin104, the semiconductor composition of the dielectric barrier 118 (e.g.,the semiconductor species and/or ratio of semiconductors) may besubstantially similar to that of the fin 104.

Referring to block 210 of FIG. 2 and to FIG. 8, any portion of thephotoresist layer 502 remaining on the workpiece 300 is removed in aphotoresist strip process. The strip process may use wet etching, dryetching, RIE, and/or ashing to remove the photoresist layer 502. Thestripping of the photoresist as well as the transportation of theworkpiece 300 between blocks 208 and 210 may further contribute to theformation of the dielectric barrier 118 within the source/drain recesses702.

Because the dielectric barrier 118 may inhibit the flow of carriersthrough an interface between the source/drain feature 108 and thechannel region 110, some of the dielectric barrier 118 may be removedfrom the channel region 110 interface by a cleaning process or othersuitable technique. The cleaning process may include any suitable numberof steps, some of which may shape the dielectric barrier 118 by removinga portion from the sides of the source/drain recesses 702 and some ofwhich may leave the dielectric barrier 118 substantially unchanged.

In an example of the latter, referring to block 212 of FIG. 2, thesource/drain recesses 702 and the remainder of the workpiece 300 may becleaned in a first cleaning process. In contrast to an etching process,the first cleaning process may be configured to remove loosely boundfilms, particulate matter, and debris. The first cleaning process mayuse any suitable wet cleaning or dry cleaning process, and in someexamples, the first cleaning process includes a wet clean wherede-ionized water (DI), SC1 (de-ionized water (DI), NH₄OH, and/or H₂O2),SC2 (DI, HCl, and/or H₂O₂), ozonated de-ionized water (DIWO₃), SPM(H₂SO₄ and/or H₂O₂), SOM (H₂SO₄ and/or O₃), SPOM, H₃PO₄, dilutehydrofluoric acid (DHF), HF, HF/ethylene glycol (EG), HF/HNO₃, NH₄OH,tetramethylammonium hydroxide (TMAH), etc. are applied to the workpiece300 including within the source/drain recesses 702. The workpiece 300and/or wet cleaning solution may be agitated using ultrasonic energy orany other technique to facilitate the cleaning process. Likewise, heatmay be applied to promote the cleaning.

In some embodiments, the first cleaning process is configured to spareat least some of the dielectric barrier 118 while removing other films,particulate matter, and/or debris. In an example where the wet cleanuses a HF-based solution, the HF is diluted within the solution to nomore than 500:1 (DI:HF) as greater concentrations of HF have beendetermined to remove the dielectric barrier 118. In further examples,agitation and heating are reduced to avoid removing the dielectricbarrier 118. These process conditions (e.g., the specific concentrationof the cleaning solution, whether to agitate and how much, whether toheat and how much, etc.) may be specifically selected to reduce thecleaning rate and make the cleaning process less time sensitive. In someexamples, this is leveraged to preserve the dielectric barrier 118within the source/drain recesses 702. In one such example, wet cleaningusing dilute HF is performed for about 10 seconds to clean the workpiece300 while preserving the dielectric barrier 118.

Referring to block 214 of FIG. 2 and to FIG. 8, the source/drainrecesses 702 and the remainder of the workpiece 300 may be cleaned in asecond cleaning process. As with the first cleaning process, the secondcleaning process may use any suitable wet cleaning or dry cleaningprocess, and in some examples, the second cleaning process includes adry clean where O₂, ozone, H₂, NF₃, noble gas(es), and/or other suitablecleaning chemistries are applied in a gas or plasma phase. In one suchexample, the second cleaning process includes a plasma cleaning processwhere NF₃ and NH₃ precursors are used to form NH₄F and NF₄FHF, which areapplied to the workpiece 300. The plasma cleaning process is followed bya baking process. During the plasma process, NH₄F may react with nativesemiconductor oxides (e.g., SiO₂) on the workpiece 300 to form acompound that transitions to a gas form during the baking process andseparates from the workpiece 300. The second cleaning process may repeatthe plasma cleaning and baking for any number of cycles, and in one suchembodiment, the second cleaning process includes three cycles of plasmacleaning and baking.

In contrast to the first cleaning process, in some embodiments, thesecond cleaning process is configured to remove a first portion of thedielectric barrier 118 from the sidewalls of the source/drain recesses702, while leaving the bottommost portion of the dielectric barrier 118at the base of the source/drain recess 702. Accordingly, when thecorresponding source/drain feature is formed, the remaining dielectricbarrier 118 will insulate the base of the source/drain feature from theremainder of the fin 104 and/or the substrate 102. The first cleaningprocess of block 212 and the second cleaning process of blocks 214 maythin the dielectric barrier 118, and after the cleaning processes havecompleted, the remaining dielectric barrier 118 may have any suitablethickness. In various examples, the final dielectric barrier 118 has athickness at its thickest point (e.g., the thickness indicated by marker708) between about 5 nm and about 10 nm.

Referring to block 216 of FIG. 2 and to FIG. 9, an epitaxial process isperformed on the workpiece 300 in order to grow source/drain features108 within the source/drain recesses 702. The epitaxy process mayinclude CVD deposition techniques (e.g., vapor-phase epitaxy (VPE)and/or ultra-high vacuum CVD (UHV-CVD)), molecular beam epitaxy, and/orother suitable processes to apply gaseous and/or liquid precursors, todeposit a semiconductor in a crystalline form within the source/drainfeatures 108. The semiconductor of the source/drain features 108 may bethe same as that of the device fin 104 and/or the surrounding substrate102 or may be different in composition or structure. For example, thesource/drain features 108 may include a different ratio of silicon togermanium than the device fin 104 in order to impart a strain on thechannel region 110 and thereby tune carrier mobility in the channelregion 110.

The source/drain features 108 may be doped with p-type dopants, such asboron or BF₂; n-type dopants, such as phosphorus or arsenic; and/orother suitable dopants including combinations thereof. In variousexamples, a SiGe-containing source/drain features 108 are implanted withboron to a concentration between about 4×10²⁰ atoms/cm³ and about 9×10²⁰atoms/cm³. In further examples, a Si-containing source/drain features108 are implanted with phosphorous to a concentration between about3×10²¹ atoms/cm³ and about 7×10²¹ atoms/cm³. The dopants may beintroduced during the epitaxial process and/or in a subsequentimplantation process (i.e., a junction implant process). An annealingprocess may be performed on the workpiece 300 to activate the dopants,such as Rapid Thermal Annealing (RTA) and/or laser annealing.

As can be seen in FIG. 9, the bases of the source/drain features 108 areseparated from the substrate 102 and the remainder of the device fin 104by the dielectric barrier 118. The dielectric barrier 118 may preventthe flow of carriers out through the base and through the portion of thefin 104 and/or substrate 102 not under control of the gate stack 112. Inthis way, the dielectric barrier 118 may reduce leakage current andthereby improve device efficiency. The dielectric barrier 118 may have acurvilinear (curved) bottom surface where the bottommost point of thedielectric barrier 118 extends any distance below the top of theisolation features 106 and accordingly, the bottommost surface of thegate stack 112. In various examples, the dielectric barrier 118 extendsbetween about 5 nm and about 10 nm below the top of the isolationfeatures 106. In such examples, the thickness of the dielectric barrier118 may be such that the top surface of the dielectric barrier extendsabove the top of the isolation features 106 and the bottommost surfaceof the gate stack 112.

It is further noted that the remainder of the source/drain features 108(e.g., along the vertical sidewalls 902) are free of the dielectricbarrier 118 and directly physically contact the channel region 110 ofthe device fin 104. In this way, carriers are free to flow through thechannel region 110 from source to drain when the gate stack 112 placesthe device in the on state.

A corresponding cross-section through the source/drain features 108 isshown in FIG. 10. As can be seen, the bottommost surfaces of thesource/drain features 108 are separated from the remainder of the fins104 and the substrate 102 by the dielectric barriers 118. For eachsource/drain feature 108 and corresponding fin 104, the respectivedielectric barrier 118 extends from an isolation feature 106 on one sideof the source/drain feature 108 and fin 104 to an isolation feature 106on the other sides of the source/drain feature 108 and fin 104. Thus,between the dielectric barrier 118 and isolation feature 106, there isno vertical carrier path from the source/drain feature 108 to theremainder of the fin 104 and the substrate 102.

Referring to block 218 of FIG. 2, the workpiece is provided for furtherfabrication. This may include replacing placeholder elements of the gatestack 112 (e.g., placeholder gate electrode 404, capping layer 406,etc.) with functional elements, forming a interconnect structureelectrically coupling the FinFETs, and other suitable fabricationprocesses.

As explained above, the alignment of the source/drain recesses 702, thedielectric barriers 118, and the isolation features 106 and the gatestack 112 may be different in other examples. In some examples describedwith reference to FIG. 11, the etching causes bottom of the source/drainrecesses 702 to be substantially coplanar with the top of the isolationfeatures. In that regard, FIG. 11 is a cross-sectional view of a portionof a workpiece 1100 taken along a device fin according to variousaspects of the present disclosure. The workpiece 1100 includes asubstrate 102, fins 104, channel regions 110, gate stacks 112 (e.g.,gate electrode 404, capping layer 406, gate spacers 408, etc.), andsource/drain features 108 substantially similar to those describedabove.

The etching of block 208 may remove any suitable amount of the fin 104to form the source/drain features 108, and in some examples, the etchingis controlled to etch to a depth such that the bottom of the dielectricbarrier 118 is substantially coplanar with the top of the isolationfeatures 106 (indicated by marker 706) and accordingly, substantiallycoplanar with the bottommost surface of the gate stack 112 (alsoindicated by marker 706).

It is further noted that the top surface of the dielectric barrier 118may have any suitable shape. In contrast to examples of FIG. 9 where thetop surface of the dielectric barrier 118 is curvilinear and concave, inthe examples of FIG. 11, the top surface of the dielectric barrier 118is substantially planar. In various examples, the top and bottomsurfaces are such that the dielectric barrier 118 has a thickness at itsthickest point (e.g., the thickness indicated by marker 1102) betweenabout 5 nm and about 10 nm.

In some examples described with reference to FIG. 12, the etching causesbottom of the source/drain recesses 702 to be above the top of theisolation features. In that regard, FIG. 12 is a cross-sectional view ofa portion of a workpiece 1200 taken along a device fin according tovarious aspects of the present disclosure. The workpiece 1200 includes asubstrate 102, fins 104, channel regions 110, gate stacks 112 (e.g.,gate electrode 404, capping layer 406, gate spacers 408, etc.), andsource/drain features 108 substantially similar to those describedabove.

The etching of block 208 may remove any suitable amount of the fin 104to form the source/drain features 108, and in some examples, the etchingis controlled to etch to a depth such that the bottom of the dielectricbarrier 118 is above the top of the isolation features 106 (indicated bymarker 706) and accordingly, substantially coplanar with the bottommostsurface of the gate stack 112 (also indicated by marker 706). The bottomof the dielectric barrier 118 may be any distance above the planedefined by the top of the isolation features 106 and the bottommostsurface of the gate stack 112 and in various examples, the bottom of thedielectric barrier 118 is between about 5 nm and about 10 nm above theplane.

The top surface of the dielectric barrier 118 may have any suitableshape. In contrast to examples of FIG. 9 where the top surface of thedielectric barrier 118 is curvilinear and concave and the examples ofFIG. 11 where the top surface of the dielectric barrier 118 issubstantially planar, in the examples of FIG. 12, the top surface of thedielectric barrier 118 is curvilinear and convex. In various examples,the top and bottom surfaces are such that the dielectric barrier 118 hasa thickness at its thickest point (e.g., the thickness indicated bymarker 1202) between about 5 nm and about 10 nm.

Thus, the present disclosure provides examples of FinFET devices with asource/drain barrier and a method for forming such devices. In someexamples, a method includes receiving a workpiece that includes asubstrate and a device fin extending above the substrate. The device finincludes a channel region. A portion of the device fin adjacent thechannel region is etched, and the etching creates a source/drain recessand forms a dielectric barrier within the source/drain recess. Theworkpiece is cleaned such that a bottommost portion of the dielectricbarrier remains within a bottommost portion of the source/drain recess.A source/drain feature is formed within the source/drain recess suchthat the bottommost portion of the dielectric barrier is disposedbetween the source/drain feature and a remainder of the device fin. Insome such examples, the cleaning of the workpiece includes a drycleaning process configured to remove a side portion of the dielectricbarrier disposed along a side surface of the source/drain recess and toleave the bottommost portion of the dielectric barrier. In some suchexamples, the cleaning of the workpiece further includes a wet cleaningprocess configured such that the dielectric barrier remains after thewet cleaning process. In some such examples, the dry cleaning processremoves the side portion of the dielectric barrier such that a sidesurface of the source/drain feature is free of the dielectric barrierand physically contacts the channel region. In some such examples, thereceived workpiece further includes a gate stack disposed on and aroundthe channel region and the etching of the portion of the device fin isperformed to a depth such that a bottommost surface of the dielectricbarrier extends to a depth below a bottommost surface of the gate stack.In some such examples, a topmost surface of the dielectric barrier isdisposed above the bottommost surface of the gate stack. In some suchexamples, the received workpiece further includes a gate stack disposedon and around the channel region, and the etching of the portion of thedevice fin is performed to a depth such that a bottommost surface of thedielectric barrier extends to a depth substantially coplanar with abottommost surface of the gate stack. In some such examples, thereceived workpiece further includes a gate stack disposed on and aroundthe channel region, and the etching of the portion of the device fin isperformed to a depth such that a bottommost surface of the dielectricbarrier extends to a depth above a bottommost surface of the gate stack.In some such examples, the received workpiece further includes anisolation feature disposed alongside the device fin, and the etching ofthe portion of the device fin is performed to a depth such that thedielectric barrier extends below a topmost surface of the isolationfeature. In some such examples, the device fin is disposed between andextends above a first isolation feature and a second isolation feature,and the dielectric barrier extends from the first isolation feature tothe second isolation feature.

In further examples, a method includes receiving a substrate and a finformed on the substrate that includes a channel region. The fin isetched to define a first source/drain recess on a first side of thechannel region and a second source/drain recess on a second side of thechannel region opposite the first side. A first insulating barrier isformed within a bottommost portion of the first source/drain recess anda second insulating barrier within a bottommost portion of the secondsource/drain recess. A first source/drain feature is epitaxially grownwithin the first source/drain recess on the first insulating barrier anda second source/drain feature is epitaxially grown within the secondsource/drain recess on the second insulating barrier. In some suchexamples, the first insulating barrier and the second insulating barrierare physically separated by the channel region. In some such examples,the first insulating barrier and the second insulating barrier do notextend underneath the channel region. In some such examples, the firstinsulating barrier and the second insulating barrier are formed by theetching of the fin to define the first source/drain recess and thesecond source/drain recess. In some such examples, the firstsource/drain recess and the second source/drain recess are cleaned afterthe etching of the fin and prior to the epitaxially growing of the firstsource/drain feature and the second source/drain feature. The cleaningis configured to leave the first insulating barrier within thebottommost portion of the first source/drain recess and the secondinsulating barrier within the bottommost portion of the secondsource/drain recess. In some such examples, the cleaning is configuredto remove a first portion of the first insulating barrier along a sidesurface of the first source/drain recess and to leave a second portionof the first insulating barrier along a bottommost surface of the firstsource/drain recess.

In further examples, a device includes a substrate, and a device findisposed on the substrate. The device fin includes a channel region, asource/drain feature adjacent the channel region, and a dielectricbarrier disposed between a bottommost portion of the source/drainfeature and the substrate. In some such examples, the device furtherincludes a gate stack disposed overwrapping the channel region of thedevice fin such that a bottommost surface of the gate stack is disposedbelow a topmost surface of the device fin, and the dielectric barrierextends below the bottommost surface of the gate stack. In some suchexamples, a side surface of the source/drain feature is free of thedielectric barrier and physically contacts the channel region. In somesuch examples, the dielectric barrier does not extend underneath thechannel region.

In further examples, a device includes a substrate and a fin disposed onthe substrate. The fin includes a first source/drain feature, a firstdielectric barrier disposed between a bottom portion of the firstsource/drain feature and the substrate, a second source/drain feature, asecond dielectric barrier disposed between a bottom portion of thesecond source/drain feature and the substrate, and a channel regiondisposed between the first source/drain feature and the secondsource/drain feature. In some such examples, a side surface of the firstsource/drain feature is free of the first dielectric barrier andphysically contacts the channel region. In some such examples, the firstdielectric barrier and the second dielectric barrier do not extendunderneath the channel region. In some such examples, the firstdielectric barrier is physically separate from the second dielectricbarrier. In some such examples, the device further includes a gate stackdisposed on the channel region such that the gate stack extends below atop surface of the fin. Each of the first dielectric barrier and thesecond dielectric barrier extends below the gate stack. In some suchexamples, the device further includes an isolation feature. The finextends above the isolation feature, and each of the first dielectricbarrier and the second dielectric barrier extends below a top surface ofthe isolation feature. In some such examples, the device furtherincludes an isolation feature. The fin extends above the isolationfeature, and each of the first dielectric barrier and the seconddielectric barrier has a bottom surface substantially coplanar with atop surface of the isolation feature. In some such examples, the finincludes a first semiconductor composition, the first dielectric barrierincludes the first semiconductor composition, and the first source/drainfeature includes a second semiconductor composition that is differentfrom the first semiconductor composition. In some such examples, thedevice further includes: a first isolation feature disposed on a firstside of the fin, and a second isolation feature disposed on a secondside of the fin. The fin extends above the first isolation feature andthe second isolation feature, and the first dielectric barrier extendsfrom the first isolation feature to the second isolation feature.

In further examples, a device includes a substrate, and a device finextending above the substrate. The device fin includes a channel region,a source/drain feature adjacent the channel region, and a dielectricbarrier disposed below the source/drain feature. The dielectric barrierhas a curvilinear bottom surface disposed at least partially below thechannel region. In some such examples, the source/drain featurephysically contacts the dielectric barrier, and the dielectric barrierphysically contacts the device fin below the dielectric barrier.

In yet further examples, a method includes, receiving a workpiece thatincludes a substrate and a fin disposed on the substrate. The finincludes a channel region and a gate stack disposed on and around thechannel region. A portion of the fin adjacent the channel region isrecessed. The recessing creates a source/drain recess and forms adielectric barrier within the source/drain recess having a curvilinearbottom surface that extends below the gate stack. The workpiece iscleaned such that a bottommost portion of the dielectric barrier thatincludes the curvilinear bottom surface remains within the source/drainrecess. A source/drain feature is formed within the source/drain recesssuch that the bottommost portion of the dielectric barrier is disposedbetween the source/drain feature and the substrate. In some suchexamples, the cleaning of the workpiece includes a dry cleaning processconfigured to remove a first portion of the dielectric barrier disposedalong a side surface of the source/drain recess and to leave thebottommost portion of the dielectric barrier.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A device comprising: a fin disposed on asubstrate, wherein the fin has a first sidewall surface and an opposingsecond sidewall surface; a first source/drain feature disposed on thefin such that the first source/drain feature physically contacts thefirst sidewall surface of the fin; and a first dielectric barrierdisposed under and interfacing with the first source/drain feature suchthat the first dielectric barrier prevents the first source/drainfeature from interfacing with the substrate below the first dielectricbarrier, wherein the first dielectric layer includes remnants of anetchant, and wherein a side surface of the first source/drain feature isfree of the first dielectric barrier.
 2. The device of claim 1, whereinthe side surface of the first source/drain feature physically contactsthe first sidewall surface of the fin.
 3. The device of claim 1, whereina channel region extends from the first sidewall surface to the secondsidewall surface.
 4. The device of claim 1, further comprising: a secondsource/drain feature disposed on the fin such that the secondsource/drain feature physically contacts the second sidewall surface ofthe fin; and a second dielectric barrier disposed under and interfacingwith the second source/drain feature such that the second dielectricbarrier prevents the second source/drain feature from interfacing withthe substrate below the second dielectric barrier.
 5. The device ofclaim 4, wherein the first dielectric barrier is spaced apart from thesecond dielectric barrier.
 6. The device of claim 1, wherein the firstdielectric barrier has a convex top surface.
 7. The device of claim 1,further comprising a gate stack wrapping around the fin.
 8. A devicecomprising: a semiconductor fin disposed over a substrate, thesemiconductor fin having a first side surface, an opposing second sidesurface, and a channel region extending from the first side surface tothe second side surface; a first source/drain feature disposed on thesemiconductor fin and physically contacting the first side surface ofthe semiconductor fin; a first dielectric barrier disposed between abottom portion of the first source/drain feature and the substrate,wherein the first dielectric barrier includes remnants of a photoresistmaterial; and a second source/drain feature disposed on thesemiconductor fin.
 9. The device of claim 8, wherein the secondsource/drain feature physically contacts the second side surface of thesemiconductor fin.
 10. The device of claim 8, further comprising asecond dielectric barrier disposed between a bottom portion of thesecond source/drain feature and the substrate.
 11. The device of claim8, wherein the first dielectric barrier has a planarized top surface.12. The device of claim 8, further comprising a shallow trench isolationstructure disposed on the substrate, wherein the shallow trenchisolation structure has a topmost surface at a first height above thesubstrate, and wherein the bottom portion of the first dielectricbarrier is positioned at a second height that is below the first heightof the topmost surface of the shallow trench isolation structure. 13.The device of claim 8, further comprising a shallow trench isolationstructure disposed on the substrate, wherein the shallow trenchisolation structure has a topmost surface at a first height above thesubstrate, and wherein the bottom portion of the first dielectricbarrier is positioned at a second height that is above the first heightof the topmost surface of the shallow trench isolation structure.
 14. Amethod comprising: removing a portion of a fin structure to form arecess in the fin structure, wherein a dielectric barrier is formed inthe recess during the removing of the portion of the fin structure,wherein the dielectric barrier includes remnants of the fin structure;removing a first portion of the dielectric barrier such that a secondportion of the dielectric barrier remains in the recess after theremoving of the first portion of the dielectric barrier; and forming asource/drain feature within the recess on the second portion of thedielectric barrier.
 15. The method of claim 14, wherein removing thefirst portion of the dielectric barrier includes performing a firsttreatment process and a second treatment process, the second treatmentprocess different than the first treatment process.
 16. The method ofclaim 14, wherein the second portion of the dielectric barrier isdisposed between the source/drain feature and a substrate, and whereinthe fin structure is disposed on the substrate.
 17. The method of claim14, further comprising forming a metal gate structure over the finstructure.
 18. The method of claim 14, wherein removing the firstportion of the dielectric barrier exposes a channel region of the finstructure.
 19. The method of claim 18, wherein forming the source/drainfeature within the recess includes forming the source/drain featuredirectly on the channel region such that the source/drain featurephysically contacts the channel region of the fin structure.
 20. Themethod of claim 14, wherein the dielectric barrier is formed in therecess during the removing of the portion of the fin structure includesforming the dielectric barrier from an etchant used during an etchingprocess performed during the removing of the portion of the finstructure.